For the purpose of analyzing the structural characteristics factor D_<eta> of metal silos, we treated the analytical models contained both the characteristics of natural period T before buckling and the ratio q of degradation of stiffness after buckling by using experimental result. As a result of the studies, the following things have obviously investigated. D_<eta> rapidly decreased and a constant before T=0.4sec and over 0.4sec, respectively. We explain the reason so that D_<eta> is influenced with T.